1. Field of the Invention
The present invention relates to a configuration of an active matrix type liquid crystal display integrated with a peripheral driving circuit.
2. Description of the Related Art
Active matrix type liquid crystal displays have been known. They have a configuration in which an active matrix circuit and a peripheral driving circuit for driving the same circuit are integrated on a glass substrate or quartz substrate.
In such a liquid crystal panel integrated with a peripheral driving circuit, a thin film semiconductor that forms thin film transistors provided in the peripheral driving circuit must be a crystalline silicon thin film. The reason for this is that the peripheral driving circuit must operate at a high speed.
Reliability is an important consideration for a liquid crystal panel integrated with a peripheral driving circuit as described above. Specifically, what is important for such a device is the stability of image display in relation to the environment where it is used.
Especially, a crystalline silicon film has a problem in that it is significantly susceptible to the variation of characteristics with time and the influence of the environment where it is used because of the high level of characteristics of itself.
Specifically, a problem arises in that it is affected by stresses exerted thereon during the fabrication and handling of a liquid crystal panel and by moisture that permeates into the liquid crystal panel.
Further, a liquid crystal panel integrated with a peripheral driving circuit is designed in an intention to minimize the surface area of regions unnecessary for screen display. For example, efforts are put in minimizing the surface area occupied by the peripheral driving circuit.
Meanwhile, in a liquid crystal display, an encapsulating material for enclosing liquid crystal, referred to as xe2x80x9csealing materialxe2x80x9d is provided at a peripheral portion to hold liquid crystal between a pair of substrates.
As an effort to minimize the surface area of regions unnecessary for screen display as described above, the surface area occupied by the sealing material must be also reduced. A configuration for this purpose is known in which a sealing material is provided on a peripheral driving circuit to minimize the surface area excluding pixels (referred to as xe2x80x9cframexe2x80x9d).
In the case of an active matrix type liquid crystal display integrated with a peripheral driving circuit, faults that occur in the peripheral driving circuit can be a problem.
Especially, the configuration in which a sealing material is provided on a peripheral driving circuit to minimize the surface area excluding pixels (referred to as xe2x80x9cframexe2x80x9d) is subjected to more faults at the peripheral driving circuit.
This problem occurs due to the following reasons. A sealing material includes a kind of spacer referred to as xe2x80x9cfillerxe2x80x9d for maintaining a gap between substrates.
In general, a peripheral driving circuit is at a high level of integration. As a result, thin film transistors and wiring lines located directly under such fillers are subjected to a pressure from the fillers (it is assumed that this pressure can be locally quite high) and are hence vulnerable to line breakage and poor contact.
Meanwhile, a spherical substrate gap maintaining means referred to as xe2x80x9cspacerxe2x80x9d is used also in an active matrix region. However, since an active matrix region is at a lower level of integration, faults attributable to the presence of a spacer are not as problematic as in a peripheral driving circuit.
It is an object of the invention disclosed in this specification to provide a configuration for an active matrix type liquid crystal display incorporating a peripheral driving circuit, in which the surface area excluding the region of a pixel matrix circuit is minimized.
On the basis of the above-described configuration, it is another object of the invention to provide a configuration that prevents breakage of thin film transistors provided on a peripheral driving circuit due to a pressure exerted by a sealing material.
It is still another object of the invention to provide a configuration for an active matrix type liquid crystal display incorporating a peripheral driving circuit, which prevents thin film transistors from being adversely affected by a stress exerted thereon during the fabrication and handling of the liquid crystal panel and which prevents moisture from permeating into the liquid crystal panel.
In order to solve the above-described problems, as a mode of carrying out the invention disclosed in this specification, there is provided an active matrix type liquid crystal display integrated with a peripheral driving circuit as shown in FIG. 1 having a configuration in which:
a sealing material 104 is provided on the peripheral driving circuit; and
resin layers 237 and 240 are provided between the peripheral driving circuit and the sealing material.
The above-described configuration makes it possible to prevent a high pressure from being locally applied to the peripheral driving circuit by a filler 103 included in the sealing material 104, thereby preventing the breakage of the peripheral driving circuit.
Further, by providing the sealing material on the peripheral driving circuit, a configuration can be obtained in which the surface area excluding the pixel region is minimized.
In the above-described configuration, each of the resin layers are preferably formed as multilayered form. This is effective in moderating the pressure exerted thereon by the filler in the sealing material.
Further, it is advantageous to form an auxiliary capacitor in the active matrix region using the resin layers. This makes it possible to provide a capacitor having a required value in a pixel.
The thickness of the resin layers is preferably equal to or greater than one-half of the diameter of a filler in the sealing material. This is a condition advantageous in preventing the pressure of a filler in the sealing material from being exerted on the peripheral driving circuit even if the filler sinks into the resin layers. Further, in order to moderate a pressure exerted on the peripheral driving circuit, a highly elastic material such as polyimide may be chosen for the resin layers. When the resin layers are formed as a multilayered form, it will be sufficient if the collective thickness is equal to or greater than one-half of the diameter of a filler in the sealing material.
In order to solve the above-described problems, as specifically illustrated in FIG. 6, there is provided a configuration in which a liquid crystal material 314 is sandwiched and held between a pair of glass substrates 301 and 318, characterized in that:
an active matrix circuit (constituted by a thin film transistor indicated by 302) and a peripheral driving circuit (constituted by a thin film transistor indicated by 303) are provided on the surface of one of the substrates 301;
a resin material is provided on the peripheral driving circuit as interlayer insulating films 306, 309, and 311;
the liquid crystal material 314 is sealed with a sealing material 315;
the resin material and the sealing material partially overlap with each other; and
the resin material is blocked from the outside by the sealing material.
In the context of the present invention, the term xe2x80x9ca surface of a substratexe2x80x9d means a surface of a glass or quartz substrate and further a surface of a glass or quartz substrate having a silicon oxide film or a silicon nitride film (so-called inorganic film) formed thereon.
The use of the above-described configuration makes it possible to moderate a stress exerted on the peripheral driving circuit and to enhance sealing capability in the region indicated by 300 in FIG. 6.
Especially, a high degree of adhesion can be achieved in the region indicated by 350 in FIG. 7 where the sealing material 315 is in contact with a silicon nitride film 305 which is an inorganic substance (inorganic film) except the region of wiring line 308. This makes it possible to achieve a high degree of adhesion in this region, thereby preventing external moisture from permeating.
In order to moderate a stress, the interlayer insulating films are preferably formed from polyimide resin. The sealing material is preferably formed from epoxy resin to enhance the sealing action further.
The interlayer insulating films can be formed without using polyimide resin.
For example, acrylic resin is also used to form the interlayer insulating film.
The active matrix type liquid crystal displays integrated with a peripheral circuit shown in FIGS. 1 and 6 are used for display devices of photographic apparatuses such as portable video movie apparatuses, portable personal computers, and various information terminals.